1. The Field of the Invention
This invention relates to moisture curable adhesives. More precisely this invention relates to means for storing and dispensing moisture curable adhesives without premature curing of the adhesive.
2. Description of the Prior Art
Various formulations for moisture curable compositions have been proposed. For example, adhesive compositions based on isocyanate terminated prepolymers have been proposed and their use in various bonding operations has also been proposed. U.K. patent specification No. 1540634 discloses inter alia the use of compositions based on certain prepolymers for bonding soles to shoes, including certain prepolymers derived from diphenyl methane diisocyanate and polyesters derived from an aliphatic dicarboxylic acid and an aliphatic diol. which are intended to be melted and supplied to the work in molten form. An adhesive composition of this kind is available from Bostik Limited under the names PA 5102 and Supergrip 2000 and is capable of use for attaching soles to shoes and various other bonding processes.
It will be apparent that moisture curable compositions are cured by reaction with moisture and it is therefore highly desirable to restrict and preferably avoid exposure of these compositions to moisture prior to use, so as to ensure a required uniformity of performance of the composition when used. It is therefore desirable to package and store the composition in a moisture proof package. It is equally important to provide for emptying of the package at the time of use to the maximum extent possible without premature cure of the composition and with minimum inconvenience to the operator even when the operator requires only a portion of the composition to be withdrawn from the package at any one time as may occur during intermittent use of the composition over a period of hours or even several days. We have found that these requirements cannot be met consistently by means of available packages and equipment. Among available equipment are various apparatuses intended to pump melted adhesive from a drum-like container via a hose connected with a piston of the apparatus which piston is adapted to be pressed into the drum to expel the melted adhesive. While this type of apparatus is generally suitable for use with many types of adhesive, we have found that when used with moisture curable adhesive, problems tend to result from seepage of the melted composition past the piston in the drum. This material hardens and adheres tenaciously to the drum and the piston and leads to not only waste of adhesive, but also difficulties in consistently preventing access of moisture of the atmosphere to adhesive in the drum. In turn this may lead to unpredictable performance of the apparatus and or adhesive during prolonged intermittent use of the apparatus to discharge adhesive from a single drum, and difficulties or inconveniences in removing the piston from the discharged drum when a fresh drum of adhesive comes to be used.
The supply of moisture curable adhesives in closed cartridges has been proposed, and may be satisfactory for small quantities of adhesive. Suitable cartridges are seamless and may be of extruded aluminum in which a tightly fitting piston may be used. However, it is desirable to provide for larger supplies of adhesive in order to permit suitable prolonged usage of a machine using the adhesive between changes from one used cartridge to another full one. Attempts to use available cans containing a piston having a peripheral skirt which trails from the piston as the piston is pushed to extrude adhesive have been unsuccessful, due to unwanted extrusion of adhesive between the skirt and the can wall.
The objects of the present invention are to provide an improved package for a meltable, moisture curable composition and to provide
apparatus for dispensing the composition from the package.